Correlation found between asymptomatic retinal arteriole emboli and CCAPs

New research showed that calcified carotid artery plaques (CCAPs) seen on panoramic images (PIs) might be life-threatening to patients. The findings contradict those of some previous studies’ authors who proposed that CCAPs seen on PIs are so extensively calcified that they can be presumed stable and thus are highly unlikely to embolize and cause a systemic event.

Unstable plaques in the cervical distribution of the carotid artery are responsible for most ischemic strokes because they release fairly large-sized embolic debris, which enters the intracerebral circulation and most commonly occludes the middle cerebral artery, the authors said in the article published in the published in the April issue of Oral Surgery, Oral Medicine, Oral Pathology and Oral Radiology. The plaques also shed smaller bits of debris, which drift to the edge of the bloodstream, enter the internal carotid artery’s first branch (the ophthalmic artery), and finally lodge in the bifurcation or narrowed segments of small retinal arterioles, the authors also said.

Because asymptomatic retinal arteriole emboli (ARAE) emanate from unstable plaques located in the region seen on the PI—the carotid bifurcation and the proximal internal carotid artery—a team of scientists from the University of California, Los Angeles and the Veterans Affairs Greater Los Angeles Healthcare System developed a study in which they enrolled patients with both panoramic and digital retinal images. Scientists were primarily looking for the presence or absence of ARAE on digital retinal images of the eye on the same side as the radiographically observed CCAPs. They compared 2 groups of patients, those with and without CCAPs on their PIs.

The retrospective, case-control study participants were patients with type 2 diabetes mellitus who had their panoramic and digital retinal imaging performed at the Los Angeles VA Affairs Medical Center from October 1, 2000, through March 20, 2015. One group consisted of patients with CCAP unilaterally (owing to the need to specifically identify the ipsilateral retina) and a digital retinal imaging study performed within 24 months of the panoramic imaging. The other group included only patients’ having PIs that were obtained bilaterally without CCAP on their PIs and with a digital retinal imaging study within the same period. Each group consisted of 50 patients matched by age and body mass index percentile.

Results showed that ARAE were found in the eye ipsilateral to the radiographically observed carotid atheroma in 10 of the 50 patients who had CCAPs compared with 2 of 50 in the group of patients who had no CCAPs. The difference, 20% versus 4%, was statistically significant.

The association of ARAE with the extent of carotid artery stenosis has been documented in a number of substantial studies, according to the authors, including recent research performed by the Mayo Clinic. In that study, the authors concluded that ARAE are a significant marker of carotid artery disease and that patients with ARAE are in need of a medical workup, including carotid ultrasonography.

Within the conclusions, the authors noted that the instability of some plaques seen on panoramic images is owing to their association ARAE. “Thus all dental patients showing CCAPs on their panoramic image should be referred for a comprehensive evaluation of their carotid vasculature as well as systemic atherogenic profile, given that previous studies have demonstrated that both CCAPs and ARAE herald future adverse cerebrovascular and cardiovascular events.

Scientists publishing in the June issue of Oral Surgery, Oral Medicine, Oral Pathology and Oral Radiology found that widened periodontal ligament space (WPLS) along the entire mandibular root length without a defined epicenter and adjacent bone destruction is a marker of irradiated bone and a common finding after head and neck radiotherapy. The findings are important because clinicians should avoid surgical procedures involving irradiated bone owing to its susceptibility to osteoradionecrosis. WPLS after radiotherapy can mimic dental inflammatory disease and dentists unaware of this jaw change may perform unnecessary endodontic therapy or dental extraction precipitating bone death.

WPLS is among 4 significant postradiotherapy changes in dental patients. “Recognition of the four post-radiotherapy jaw changes may underscore the need for conservative dental treatment and preventive measures, such as fluoride application and good oral hygiene, to reduce the risk of dental inflammatory disease,” the authors said.

To document the frequency of these mandibular changes—WPLS, bone sclerosis, periodontal disease–like bone loss and bone resorption—on panoramic imaging, a multispecialist team of scientists conducted a retrospective study. From the records of 1,859 patients with head and neck cancer who received preradiotherapy dental care and intensity-modulated radiotherapy (IMRT) at the Princess Margaret Hospital in Toronto from 2005 through 2008, 151 met the study inclusion criteria of a minimum of 2 panoramic images (at least 1 taken before IMRT) and available medical and dental records. Of these 151 patients, 25 were deemed ineligible owing to osteoradionecrosis or indeterminable IMRT dose data.

Of a total of 292 images from the remaining 126 patients, the first pre-IMRT baseline panoramic image for each patient was compared with post-IMRT images (166) by 3 observers independently—2 oral and maxillofacial radiologists and 1 radiology resident—all who did not have access to medical histories or imaging reports. They recorded findings on the pre-IMRT baseline image that resembled the 4 postradiotherapy jaw changes to distinguish them from post-IMRT findings and reached a consensus on the definition and appearance of these bone changes.

Results showed that of the 126 patients, 75 (60%) had post-IMRT mandibular changes on panoramic images that were not in the pre-IMRT images and 51 (40%) did not. Detected changes included WPLS (88%), bone sclerosis (32%), periodontal disease–like bone loss (11%), and bone resorption (11%). The average time to WPLS after IMRT was 29 months. Both female sex and dose correlated with decreased time to WPLS.

In the discussion, the authors noted that the estimated cumulative incidence rate of WPLS in the first year after IMRT might be low because some 80% of the first follow-up panoramic images were dated more than 1 year after IMRT. “Thus the incidence of post-IMRT WPLS reported here might be an underestimation of the true time of incidence,” the authors said. They called for future studies with larger sample sizes and more fixed time intervals between imaging for more accurate determination of WPLS incidence.

Researchers said the reason for earlier incidence of WPLS among females is unclear, though may be attributed to the immunologic differences between males and females. Results also showed that radiation dose had a significant effect on WPLS over time, with doses of 45 gray or greater related to earlier jaw change after IMRT compared with doses of less than 45 Gy.

“Postradiotherapy WPLS changes should be recognized and differentiated from both the odontogenic-related and cancer-induced types of WPLS,” the authors advised in the conclusions. “Treatment, extraction in particular, of teeth with post-radiotherapy WPLS is not required, as surgery is an established risk factor of osteoradionecrosis.”

This was the first large case-series study to document and characterize subclinical mandibular changes visible on panoramic imaging after head and neck radiotherapy. Before this research, there had been only 2 case reports about resulting jaw changes.

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The benefit of thyroid shielding

The thyroid gland is one of the most radiosensitive organs in the head and neck region. Preventing radiation of the organ by using a thyroid shield when performing intraoral radiography has been supported often in the literature and recommended by professional organizations such as the American Dental Association and the American Thyroid Association.

However, guidelines on radiation protection in dentistry are divided on the use of thyroid protection—a “remarkable” circumstance—according to scientists in the Department of Oral and Maxillofacial Radiology at the Academic Centre for Dentistry Amsterdam, Amsterdam, The Netherlands, in an article published online April 14 in Dentomaxillofacial Radiology. They surmised that there is a perception that with the use of rectangular collimation, the thyroid dose is already considerably reduced and that such an assessment could be a possible reason for a lack of consensus and reflected in what they termed “ambiguous” advice in the European Guidelines. They state, “It is probable that rectangular collimation for intraoral radiography offers similar level of thyroid protection to lead shielding, in addition to its other dose reducing effects.” On the other hand, the document also states, “Lead shielding of the thyroid gland should be used in those cases where the thyroid is in line of, or very close to the primary beam.” Such is the case in intraoral radiography of the upper anterior region so researchers deduce the latter recommendation contradicts the former.

“In light of the lack of clarity considering the guidelines, the utility of thyroid shield in intraoral radiography needs further investigation,” they said. “Especially, the question of its yield is still worthwhile when rectangular collimation is used.”

Researchers aimed to compare the dose levels in the area of the thyroid gland for protocols with and without thyroid shield when rectangular collimation or round collimation is used during bitewing and periapical images are obtained in different maxillary regions. To investigate, they used a dosimeter to measure the absorbed dose level at the position of the thyroid gland with an adult male phantom. Four protocols were tested: round collimation and rectangular collimation both with and without thyroid shields. Five exposure positions were measured: maxillary incisor, maxillary canine, maxillary premolar, maxillary molar, and posterior bitewing. Exposures were repeated 10 times.

Researchers found that use of rectangular collimation without thyroid shield resulted in a large reduction of dose level to the thyroid in comparison with round collimation. Except for the maxillary incisor exposures, all exposures performed with rectangular collimation without thyroid shield resulted in a lower thyroid dose level than those with round collimation with thyroid shield, indicating a clear relationship between rectangular collimation and more effective thyroid shielding. Furthermore, the thyroid shield contributed substantially to the dose level reduction of rectangular collimation for maxillary anterior and canine exposures and marginally reduced (by 10% or less) the thyroid dose level for the other exposures.

In conclusion, the authors advised that the thyroid shield is a sensible dose-reducing measure when obtaining images of maxillary anterior teeth, even when rectangular collimation is used. “For children, this advice should be even more stringent,” they counseled.

Cone-beam computed tomographic (CBCT) images can provide a reliable analysis of the upper airway that can be used to diagnose breathing disorders such as obstructive sleep apnea, according to a report published in the July issue of Oral Surgery, Oral Medicine, Oral Pathology and Oral Radiology. The research described a method for anatomic landmark localization that provided high intraobserver and interobserver reliability in a retrospective study.

Scientists in The Netherlands found that most of the landmarks chosen in previous studies were cephalometric, using only the hard-tissue landmarks and excluding those of the soft tissue related to the upper airway. In addition, much of the previous research focused solely on the reliability of the volume of the upper airway, without testing the reliability of the area measurement or that of the linear measurement. Therefore, the team aimed to assess reliability of the localization of both hard-tissue and soft-tissue landmarks, as well as 3-dimensional measurements based on these landmarks.

Their study included CBCT images of 15 patients who were randomly selected from scans available at the Department of Oral and Maxillofacial Radiology of the Academic Centre for Dentistry Amsterdam, The Netherlands. Images covered the entire upper airway from the level of the hard palate to the base of the epiglottis. All patients had been referred for an examination of the temporomandibular joints from April 1, 2013, through July 1, 2014. Two oral maxillofacial radiologists and 1 orthodontist independently localized 5 landmarks—posterior nasal spine, anterior nasal spine, anteroinferior aspect of the vertebral body of the second cervical vertebra, tip of the uvula, tip of the epiglottis, and the base of the epiglottis—using the axial sagittal and coronal planes of the CBCT data sets.
Results showed that calculations of intraobserver and interobserver reliability of the anatomic landmark localization and of the upper airway measurements were excellent.

Among discussion points, the authors noted that CBCT has an increasingly important role in the diagnosis of morphologic abnormalities in the oral and maxillofacial region. “Although it does not have the same excellent soft tissue contrast as magnetic resonance imaging, it was shown in our study that there was an excellent reliability of the localization of the soft tissue landmarks, such as the tip of the uvula and the tip of the epiglottis.”

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News You Can Use

Convey the value of x-rays with ADA brochure

When a patient asks why radiographs are needed, the ADA has a brochure to explain the reasons. “Dental X-Ray Exams: Answers to Common Questions” explains that finding and treating dental problems at an early stage can save time and money and prevent pain.

The handout assures patients of the safety of X-rays and shows how dental offices take steps to reduce radiation exposure. This six-panel brochure features X-ray images and comes in packs of 50, with volume discounts available. Members can preview “Dental X-Ray Exams” online. To order, call 1-800-947-4746 or go to adacatalog.org. Readers who use the code 16402E before August 31 can save 15 percent on all ADA Catalog products.

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What is Specialty Scan?

This is one in a series of quarterly newsletters updating dentists on selected specialties in dentistry. Information presented is aggregated and summarized from previously published materials, each item attributed to its publication of origin. This issue of JADA Specialty Scan focuses on oral and maxillofacial radiology, the third in the series on this topic for 2016. Other Specialty Scan issues are devoted to endodontics, oral pathology, orthodontics, periodontics and prosthodontics. The ADA has engaged the specialty organizations in these areas as well as its own Science Institute and Division of Legal Affairs to assist with these newsletters. We welcome feedback on this and all Specialty Scan issues.

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